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Thread: A nice informative piece on Z32 suspension.

          
   
  1. #1
    Club Guest MarTTy4653's Avatar
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    A nice informative piece on Z32 suspension.

    This was written up by Ash from Z1.

    This will be a long read with a lot of explanation, of which you may know nothing about, a little about, or may even be beyond in the understanding, so bear with me..

    Well, I took the Z to Pep Boys today for a much needed alignment. About a month ago I put a 60K mile NA rear end on my Z as the original was wearing out and there was excessive play in just about every bushing.. My chassis has 178,8xx miles on it and the rear was just worn out. The car that the subframe was pulled from had front end damage, but apparently the wrecker (flatbed) pulled the wrecked car up by the rear toe adjustment link of the rear suspension and bent them both pretty good.. So I swapped them out for a good pair.. But by doing this, the installation of the new pieces required me to 'guess' at the toe correction and I knew it wasn't right.

    About 2 months ago I put our noltec front upper adjustable a-arms on to correct the camber as it was off.

    For those of you who have had experience with higher mileage Z's, you will know that the front of the car has a design flaw. It has to do with the framing rails, upper fender rails, and the wheel well buckets.. It allows the top of the shock towers (the wheel well buckets, where the shock absorber attaches and where the upper a-arm attaches), and over time, pothole after pothole, and aftermarket (stiffer) suspension literally beats the shock towers in towards the engine (centerline of the car). This causes the camber to become increasingly more negative (top of wheel leans inward) and the only way to properly correct this is to take it to a frame shop and have them pull it out.. Then you can use a high quality strut tower brace (carbing is the only one that has my recommendation as it doesn't go right over the metal fuel lines and wear into them and its built exceptionally well). The brace will keep this problem from occuring.

    However, if you lower your car, which I have, using the Eiback Pro-Kit, it will add negative camber into the suspension. The only way to combat this is to install upper adjustable a-arms in both front and rear. Although the rear upper links are adjustable, they aren't adjustable enough to achieve a good camber for your now-stiffer suspension.

    My car drove erratically on the interstate; wanting to 'cat' around the road as deviations in the road from heavy trucks 'pressing' tracks where their wheels run and uneven/unlevel joints caused from crappy paving processes.. I knew the toe was off, but I found a few other things wrong once we put it on the alignment rack.

    The suspension in my car is lowered, stiffer by springs, and stiffer (rollwise) due to the Suspension Techniques sway bars. The factory specifications of the suspension angles is based on factory springs, factory shocks, and factory sway bars, so there are deviations from those parameters you will need to make in order to get the car to properly 'hook up' while cornering.

    As the car rolls when you turn, or the lack of as much roll now that you have all these suspension upgrades, the camber required to keep the tires in as much contact with the road lessens so you will want to request there to be less camber in the front and rear of the suspension. The service spec is as follows:

    Rear camber: -1.7 to -0.7 degrees

    Since I dont have aftermarket upper rear adjustable a-arms and my car is lowered, we could only adjust it out to -1.6 degrees on both left and right sides. Although this is still within the factory limit, its not as much as I would have liked to have gotten it closer to 0 degrees.

    One of the nice things about stiffer suspension is that because of less body roll, it requires less camber to maintain a larger tire patch, which also benefits you if you drag race. Since the camber is already negative when the car is sitting still, you aren't distributing the pressure evenly across the tire patch, which means you aren't getting as much traction on launches. Before the subframe swap I had the rear suspension set to -0.2 degrees camber specifically to try and keep the patch pressure equal to get the best traction off the line (and I was pulling sub 2.0 second 60' times on 245 series street tires). Once we adjusted the rear camber as much as possible today, it has come apparent that you NEED upper adjustable a-arms if you lower the car AND want to have proper camber (which will actually be less than what Nissan spec is).

    So the front suspension is another interesting situation as well with the lowering of the car and the upper adjustable a-arms to combat the camber problem - it screws with the caster. Fortunately I also have adjustable tension rods, which allow you to change the caster.

    Caster is the angle of which the hub 'leans', like the front rake of a motorcycle or bicycle. As the wheels are turned during cornering, this 'rake' causes the wheel to lean, which is beneficial during cornering as the idea here is to match the wheel's angle of lean to body roll so that the tire maintains the best tire patch/most traction. Additionally, if you are braking into a corner, the weight shifts to the front of the car, it noses in a little, and as the upper a-arm comes up, it adds more camber to the tire to keep it at the correct angle to the ground.

    But the upper adjustable a-arms present an issue with camber; the more you fix your camber using them, the more you affect your caster adjustment. This is because the upper a-arm doesn't run perpendicular from the centerline of the car - in fact, its closer to a 45 degree angle, pointing more forward. So as you lengthen this piece to correct the camber, you are also moving the top of the hub forward, which lessens caster. I think Nissan actually did it this way for a specific reason; as you stiffen the suspension, you will need less caster, and since stiffening the suspension typically means you are going to shorter and stiffer springs, it only serves to help with designing it this way to ease future adjustability once you make a change from the original design.. This may just have been a nice secondary effect to the original design - I would imagine there is more of a dynamic going on in the suspension that made them build it that way... Regardless, it works to our advantage because as you stiffen the suspension, you will need less caster to compensate for body roll and nose-dive.

    The factory specs for camber are as follows:
    Front camber: -1.6 to -0.1 degrees.

    Factory specs for caster are as follows:

    Front caster: 9.0 to 10.5 degrees

    Front camber is easily adjusted by shortening or lengthening the adjustable a-arms, but remember that this affects caster; the longer that upper arm has to be to bring the top of the wheel out (less negative camber), the less caster you are going to have.

    My camber was pretty spot on, right at -1.0, but because the suspension is stiffer and there will be less body roll, you dont want that much camber.. So I had the tech pull them out to the minimum spec, putting them at -0.1 degrees. They are for all practical purposes, straight up and down.

    But then we get to the caster.. Measuring it after a full sweep showed 6.1/5.9 degrees (L/R). Looking at the wheel's position in the well, they were both pretty centered, only slightly closer to the front of the wheel well.. With the adjustable tension rods, we began shortening the rods to get more caster, but even at their full adjustment, we could only get them up to a little under 7 degrees; we simply couldn't get any more, and although not excessive, the wheel was approaching closer to the front of the well.. Any more and it would start looking funny and perhaps cause a little bit of scrub with the wheel well liner. Then I started thinking a little more about what all this post is about; the fact that the stock settings will no longer apply once you mod just about every element of the suspension short of putting a porsche transaxle on it.

    So I decided to put them both at 6 degrees, 3 degrees less than the minimum spec of which Nissan suggests for the stock setup; being 66% of the factory spec. This may or may not be a sound explanation, but I would suspect that my car only has around 66% or so of its original roll and nose-dive (maybe even more), and the caster is directly linked to body roll. In what exact amount I'm not terribly certain about, but I'm sure I'm going in the right direction by lessening caster.. The fact that it also keeps the wheel pretty much centered in the well was a deciding factor because I dont want wheel scrub with the liner, but I think it will also be beneficial to handling capability...

    I'm not sure if this is your average run-of-the-mill knowledge, but it seems to me that if you are going to do anything with your suspension, you have got to do just about everything short of that Porsche transaxle conversion in order to do it right else you risk hurting the dynamics of the suspension more than actually help it..

    I'm not sure what the companies that build these aftermarket suspension pieces recommend for toe/camber/caster, but I know enough to say that it is imperative that you use something other than factory specs. I also have Greg Dupree subframe spacers, which are changing the relationship between the front and rear suspension (since the rear subframe floats), different brakes, etc... what would be the suggested settings when you begin modifying the elements of your suspension?.. and I guess that's the main reason for this post... Just thought I'd share my thoughts on the subject..

  2. #2
    Nvm

  3. #3
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    Give me a minute and I'll look at the Z32 rear suspension again...

    For one Eibach Pro Kits are not nearly stiff enough to inhibit roll enough to restrict the car from working through it's camber curve. The original poster obviously is much more into drag racing than any other form of motorsports as no one that drove for something that required turning would only want .5 degree of camber.

    The Z32 still has too much anti dive built into the suspension which is largely what is causing his excessive front to real roll upon braking/acceleration due to LCA angle.

    The Dupree spacers do very little to offset the suspension any more than returning the subframes location to what it was when new.

    What are the factory alignment specs for the Z?

  4. #4
    IMO, Ash is out of his area of expertise here.

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